@article{FoehrenbacherKrahfussZapfetal.2021,
  author    = {F{\"o}hrenbacher, Steffen A. and Krahfuss, Mirjam J. and Zapf, Ludwig and Friedrich, Alexandra and Ignat'ev, Nikolai V. and Finze, Maik and Radius, Udo},
  title     = {Tris(pentafluoroethyl)difluorophosphorane: a versatile fluoride acceptor for transition metal chemistry},
  series = {Chemistry Europe},
  volume    = {27},
  journal   = {Chemistry Europe},
  number    = {10},
  doi       = {10.1002/chem.202004885},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256665},
  pages     = {3504-3516},
  year      = {2021},
  abstract  = {Fluoride abstraction from different types of transition metal fluoride complexes [L\(_n\)MF] (M=Ti, Ni, Cu) by the Lewis acid tris(pentafluoroethyl)difluorophosphorane (C\(_2\)F\(_5\))\(_3\)PF\(_2\) to yield cationic transition metal complexes with the tris(pentafluoroethyl)trifluorophosphate counterion (FAP anion, [(C\(_2\)F\(_5\))\(_3\)PF\(_3\)]\(^-\)) is reported. (C\(_2\)F\(_5\))\(_3\)PF\(_2\) reacted with trans-[Ni(iPr\(_2\)Im)\(_2\)(Ar\(^F\))F] (iPr2Im=1,3-diisopropylimidazolin-2-ylidene; Ar\(^F\)=C\(_6\)F\(_5\), 1 a; 4-CF\(_3\)-C\(_6\)F\(_4\), 1 b; 4-C\(_6\)F\(_5\)-C\(_6\)F\(_4\), 1 c) through fluoride transfer to form the complex salts trans-[Ni(iPr\(_2\)Im)\(_2\)(solv)(Ar\(^F\))]FAP (2 a-c[solv]; solv=Et\(_2\)O, CH\(_2\)Cl\(_2\), THF) depending on the reaction medium. In the presence of stronger Lewis bases such as carbenes or PPh\(_3\), solvent coordination was suppressed and the complexes trans-[Ni(iPr\(_2\)Im)\(_2\)(PPh\(_3\))(C\(_6\)F\(_5\))]FAP (trans-2 a[PPh\(_3\)]) and cis-[Ni(iPr\(_2\)Im)\(_2\)(Dipp\(_2\)Im)(C\(_6\)F\(_5\))]FAP (cis-2 a[Dipp\(_2\)Im]) (Dipp\(_2\)Im=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were isolated. Fluoride abstraction from [(Dipp\(_2\)Im)CuF] (3) in CH\(_2\)Cl\(_2\) or 1,2-difluorobenzene led to the isolation of [{(Dipp\(_2\)Im)Cu}\(_2\)]\(^2\)\(^+\)2 FAP\(^-\) (4). Subsequent reaction of 4 with PPh\(_3\) and different carbenes resulted in the complexes [(Dipp\(_2\)Im)Cu(LB)]FAP (5 a-e, LB=Lewis base). In the presence of C6Me6, fluoride transfer afforded [(Dipp\(_2\)Im)Cu(C\(_6\)Me\(_6\))]FAP (5 f), which serves as a source of [(Dipp\(_2\)Im)Cu)]\(^+\). Fluoride abstraction of [Cp\(_2\)TiF\(_2\)] (7) resulted in the formation of dinuclear [FCp\(_2\)Ti(μ-F)TiCp\(_2\)F]FAP (8) (Cp=η\(^5\)-C\(_5\)H\(_5\)) with one terminal fluoride ligand at each titanium atom and an additional bridging fluoride ligand.},
  language  = {en}
}
@article{ZapfRadiusFinze2021,
  author    = {Zapf, Ludwig and Radius, Udo and Finze, Maik},
  title     = {1,3-bis(tricyanoborane)imidazoline-2-ylidenate anion - a ditopic dianionic N-heterocyclic carbene ligand},
  series = {Angewandte Chemie International Edition},
  volume    = {60},
  journal   = {Angewandte Chemie International Edition},
  number    = {33},
  doi       = {10.1002/anie.202105529},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256498},
  pages     = {17974-17980},
  year      = {2021},
  abstract  = {The 1,3-bis(tricyanoborane)imidazolate anion 1 was obtained in high yield from lithium imidazolate and B(CN)\(_3\)-pyridine adduct. Anion 1 is chemically very robust and thus allowed the isolation of the corresponding H\(_5\)O\(_2\)\(^+\) salt. Furthermore, monoanion 1 served as starting species for the novel dianionic N-heterocyclic carbene (NHC), 1,3-bis(tricyanoborane)imidazoline-2-ylidenate anion 3 that acts as ditopic ligand via the carbene center and the cyano groups at boron. First reactions of this new NHC 3 with methyl iodide, elemental selenium, and [Ni(CO)\(_4\)] led to the methylated imidazolate ion 4, the dianionic selenium adduct 5, and the dianionic nickel tricarbonyl complex 6. These NHC derivatives provide a first insight into the electronic and steric properties of the dianionic NHC 3. Especially the combination of properties, such as double negative charge, different coordination sites, large buried volume and good σ-donor and π-acceptor ability, make NHC 3 a unique and promising ligand and building block.},
  language  = {en}
}
@article{ZapfPetersBertermannetal.2022,
  author    = {Zapf, Ludwig and Peters, Sven and Bertermann, R{\"u}diger and Radius, Udo and Finze, Maik},
  title     = {Tricyanoborane-Functionalized Anionic N-Heterocyclic Carbenes: Adjustment of Charge and Stereo-Electronic Properties},
  series = {Chemistry - A European Journal},
  volume    = {28},
  journal   = {Chemistry - A European Journal},
  number    = {39},
  doi       = {10.1002/chem.202200275},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-287200},
  year      = {2022},
  abstract  = {The 1-methyl-3-(tricyanoborane)imidazolin-2-ylidenate anion (2) was obtained in high yield by deprotonation of the B(CN)3-methylimidazole adduct 1. Regarding charge and stereo-electronic properties, anion 2 closes the gap between well-known neutral NHCs and the ditopic dianionic NHC, the 1,3-bis(tricyanoborane)imidazolin-2-ylidenate dianion (IIb). The influence of the number of N-bonded tricyanoborane moieties on the σ-donating and π-accepting properties of NHCs was assessed by quantum chemical calculations and verified by experimental data on 2, IIb, and 1,3-dimethylimidazolin-2-ylidene (IMe, IIa). Therefore NHC 2, which acts as a ditopic ligand via the carbene center and the cyano groups, was reacted with alkyl iodides, selenium, and [Ni(CO)\(_{4}\)] yielding alkylated imidazoles 3 and 4, the anionic selenium adduct 5, and the anionic nickel tricarbonyl complex 8, respectively. The results of this study prove that charge, number of coordination sites, buried volume (\%V\(_{bur}\)) and σ-donor and π-acceptor abilities of NHCs can be effectively fine-tuned via the number of tricyanoborane substituents.},
  language  = {en}
}
@article{FoehrenbacherZehKrahfussetal.2021,
  author    = {F{\"o}hrenbacher, Steffen A. and Zeh, Vivien and Krahfuss, Mirjam J. and Ignat'ev, Nikolai V. and Finze, Maik and Radius, Udo},
  title     = {Tris(pentafluoroethyl)difluorophosphorane and N-Heterocyclic Carbenes: Adduct Formation and Frustrated Lewis Pair Reactivity},
  series = {European Journal of Inorganic Chemistry},
  volume    = {2021},
  journal   = {European Journal of Inorganic Chemistry},
  number    = {20},
  doi       = {10.1002/ejic.202100183},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-257386},
  pages     = {1941-1960},
  year      = {2021},
  abstract  = {The synthesis and characterization of Lewis acid/base adducts between tris(pentafluoroethyl)difluorophosphorane PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) and selected N-heterocyclic carbenes (NHCs) R\(_{2}\)Im (1,3-di-organyl-imidazolin-2-ylidene) and phosphines are reported. For NHCs with small alkyl substituents at nitrogen (R=Me, nPr, iPr) the adducts NHC ⋅ PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) (2 a-h) were isolated. The reaction with the sterically more demanding NHCs Dipp\(_{2}\)Im (1,3-bis-(2,6-di-iso-propylphenyl)-imidazolin-2-ylidene) (1 i) and tBu\(_{2}\)Im (1,3-di-tert-butyl-imidazolin-2-ylidene) (1 j) afforded the aNHC adducts 3 i and 3 j (a denotes "abnormal" NHC coordination via a backbone carbon atom). The use of tBuMeIm (1-tert-butyl-3-methyl-imidazolin-2-ylidene) (1 m) led to partial decomposition of the NHC and formation of the salt [tBuMeIm-H][MeIm ⋅ PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\)] (4 m). The phosphorane PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) forms adducts with PMe\(_{3}\) but does not react with PPh\(_{3}\) or PCy\(_{3}\). The mer-cis isomer of literature-known Me\(_{3}\)P ⋅ PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) (5 a) was structurally characterized. Mixtures of the phosphorane PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) and the sterically encumbered NHCs tBu\(_{2}\)Im, Dipp\(_{2}\)Im, and Dipp\(_{2}\)Im\(^{H2}\) (1,3-bis-(2,6-di-iso-propylphenyl)-imidazolidin-2-ylidene) (1 k) showed properties of FLPs (Frustrated Lewis Pairs) as these mixtures were able to open the ring of THF (tetrahydrofuran) to yield NHC-(CH\(_{2}\))\(_{4}\)O-PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\) 6 i-k. Furthermore, the deprotonation of the weak C-H acids CH\(_{3}\)CN, acetone, and ethyl acetate was achieved, which led to the formation of the corresponding imidazolium salts and the phosphates [PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\)(CH\(_{2}\)CN)]\(^{-}\) (7), [PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\)(OC(=CH\(_{2}\))CH\(_{3}\))]\(^{-}\) (8) and [PF\(_{2}\)(C\(_{2}\)F\(_{5}\))\(_{3}\)(CH\(_{2}\)CO\(_{2}\)Et)]\(^{-}\) (9).},
  language  = {en}
}